Fairly good
I'm a sucker for upgrades, and I'm glad this is the kind of game where I can upgrade everything. It was a nice idea with a decent story, though you probably could have done a bit more with both.
There was one flaw that made the game rather frustrating: There was no discernable difference in the speed of the basic attack. The clouds moved at the same speed and it fired at the same speed, even after maxing it out. This may be a glitch, and I hope it gets fixed for anyone else who wants to play it. I've already beaten the game.